An assembly line is a physical space in a manufacturing process in which parts are added to a product in a sequential manner to create a finished product. A manufacturing process which uses an assembly line is sometimes referred to as a progressive assembly process. Assembly lines are designed for the sequential organization of workers and/or robots operating tools for the combination of, modification of, or enhancements of, parts or work-pieces on the assembly line on a station-by-station basis. An assembly line is often much faster than individually handcrafting each product from start to finish when manufacturing a large number of products, and often with more controlled quality and uniformity. The motion of workers is minimized to the extent possible, and most parts or assemblies are handled either by conveyors or motorized vehicles, or gravity, with little manual trucking.
Henry Ford is often attributed with the early success of the Assembly line with the production of the Model T automobile. In My Life and Work, a book written by Henry Ford in collaboration with Samuel Crowther and published by Garden City Publishing in 1922, Henry Ford states that the principles of assembly are these: “(1) Place the tools and the men in the sequence of the operation so that each component part shall travel the least possible distance while in the process of finishing. (2) Use work slides or some other form of carrier so that when a workman completes his operation, he drops the part always in the same place—which place must always be the most convenient place to his hand—and if possible have gravity carry the part to the next workman for his operation. (3) Use sliding assembling lines by which the parts to be assembled are delivered at convenient distances.”
Even with the tools and men in sequence so that the parts travel the least distance, use of work slides and carriers so the part is always in the same place, and using of convenient distances, tools and equipment on the assembly line may still contact the parts and work-pieces on the assembly line. When a tool, part, or piece of equipment contacts a painted surface of a work-piece on the assembly line a chip or scratch may occur. This paint damage may require additional processing at the end of the assembly line to repair the chip or scratch.